The present invention relates to a method of manufacturing a layer with electrical conductivity comprising a polymer, in which a polymerized pyrrole is anchored.
In, for example, transformers with a high direct voltage level, great differences in electrical conductivity between the oil or other used insulating fluid and the solid insulating material, such as pressboard and paper, lead to considerable problems. The solid insulating material is charged to a very considerable extent, which must be taken into consideration when dimensioning the solid insulating material and which involves considerable disadvantages. These problems could be eliminated, or in any case be considerably reduced, by the use of solid insulating materials with a suitably adapted surface conductivity. Similar problems to achieve a suitably adapted surface conductivity exist, inter alia, in connection with bushings in d.c. and a.c. insulation systems and along insulating bodies in general.
From U.S. Pat. No. 4,521,450 it is known to increase the electrical conductivity of solid impregnable materials, such as cellulose-based insulating materials, by polymerizing pyrrole or N-methylpyrrole in contact with the insulating material in such a way that the polymerized pyrrole compound becomes electrically conductive. This can be done by impregnating the insulating material, before adding the pyrrole compound, with an aqueous solution of a ferric compound or another substance with the ability to give an electrically conductive polymerized pyrrole upon polymerization of the pyrrole compound. The pyrrole compound can be supplied to the insulating material in gaseous or liquid state.
It is also known, from Synthetic Metals, 10 (1984/85), 67-69, to bring about a conductive film by the use of pyrrole. In that case a film of polyvinyl alcohol is applied to an electrode and the applied polyvinyl alcohol is heat-treated so as to become sufficiently insoluble but swellable in water. The electrode is then placed together with a second electrode in an electrolyte in the form of an aqueous solution containing pyrrole. The pyrrole is thereafter subjected to electrochemical polymerization, which takes place while the pyrrole is anchored to the film of polyvinyl alcohol.
Conducting films can also be manufactued from copolymers of isoprene and acetylene, which is clear from the J. Chem. Soc., Chem. Commun. 1984, 1347-48. In that case the conducting polymer is dissolved in an organic solvent and is cast to a film. However, the copolymer is not stable in air, so the manufacture of the film must be carried out in an inert atmosphere and the use of the film is strictly limited.